Use default dimension data for defaulted registry entry

api/src/main/java/com/viaversion/viaversion/api/minecraft/RegistryEntry.java

@@ -25,6 +25,12 @@ package com.viaversion.viaversion.api.minecraft;
 import com.viaversion.nbt.tag.Tag;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
+/**
+ * Represents an entry in a registry.
+ *
+ * @param key key of the registry entry
+ * @param tag data of the registry entry, or null if the client should use its default
+ */
 public record RegistryEntry(String key, @Nullable Tag tag) {
 
     public RegistryEntry withKey(final String key) {

common/src/main/java/com/viaversion/viaversion/data/entity/DimensionDataImpl.java

@@ -48,6 +48,14 @@ public final class DimensionDataImpl implements DimensionData {
         this.minY = minY.asInt();
     }
 
+    public static DimensionData withDefaultsFor(final String key, final int id) {
+        return switch (key) {
+            case "overworld", "overworld_caves" -> new DimensionDataImpl(id, -64, 384);
+            case "the_nether", "the_end" -> new DimensionDataImpl(id, 0, 256);
+            default -> throw new IllegalArgumentException("Missing registry data for unknown dimension: " + key);
+        };
+    }
+
     @Override
     public int id() {
         return id;

common/src/main/java/com/viaversion/viaversion/rewriter/EntityRewriter.java

@@ -527,7 +527,11 @@ public abstract class EntityRewriter<C extends ClientboundPacketType, T extends
             final Map<String, DimensionData> dimensionDataMap = new HashMap<>(entries.length);
             for (int i = 0; i < entries.length; i++) {
                 final RegistryEntry entry = entries[i];
-                dimensionDataMap.put(Key.stripMinecraftNamespace(entry.key()), new DimensionDataImpl(i, (CompoundTag) entry.tag()));
+                final String key = Key.stripMinecraftNamespace(entry.key());
+                final DimensionData dimensionData = entry.tag() != null
+                    ? new DimensionDataImpl(i, (CompoundTag) entry.tag())
+                    : DimensionDataImpl.withDefaultsFor(key, i);
+                dimensionDataMap.put(key, dimensionData);
             }
             tracker(connection).setDimensions(dimensionDataMap);
         }